Charge pump circuits

ABSTRACT

A charge pump circuit includes a voltage output terminal, a flying capacitor, and a current source. The flying capacitor includes a first terminal coupled to the voltage output terminal, and a second terminal coupled to an output terminal of a drive circuit. The current source includes a first terminal coupled to the voltage output terminal, and a second terminal coupled to a power supply rail.

CROSS-REFERENCE TO RELATED APPLICATIONS

This continuation application claims priority to U.S. patent applicationSer. No. 16/663,481, filed Oct. 25, 2019, which claims the benefit ofand priority to U.S. Provisional Patent Application No. 62/777,987,filed Dec. 11, 2018, both of which are incorporated herein by referencein their entirety.

BACKGROUND

Many electronic circuits apply multiple power supply voltages. In caseswhere a power supply voltage is lightly loaded, a charge pump circuitmay be used to generate the voltage. For example, in a circuit thatapplies a positive power supply voltage and a negative power supplyvoltage, a charge pump circuit may used to generate the negative powersupply voltage from the positive power supply voltage when the negativepower supply voltage is lightly loaded. Charge pump circuits useswitched capacitors to convert an input voltage to an output voltagethat may be higher than, or negative relative to, the input voltage. Ina charge pump circuit, switches coupled to a capacitor are operated insequence to first charge the capacitor from the input voltage and thentransfer the charge to the output.

SUMMARY

A charge pump circuit that includes regulation using forward and reversecurrents is disclosed herein. In one example, a charge pump circuitincludes a voltage output terminal, a flying capacitor, and a currentsource. The flying capacitor includes a first terminal coupled to thevoltage output terminal, and a second terminal coupled to an outputterminal of a drive circuit. The current source includes a firstterminal coupled to the voltage output terminal, and a second terminalcoupled to a power supply rail.

In another example, a charge pump circuit includes a voltage outputterminal, a voltage inverter circuit, and a current source. The voltageinverter circuit is coupled to the voltage output terminal and isconfigured to generate a negative voltage at the voltage outputterminal. The current source is coupled to the voltage output terminaland is configured to increase a voltage at the voltage output terminalresponsive to the voltage at the voltage output terminal being less thanthe negative voltage generated by the voltage inverter circuit.

In a further example, an electronic circuit includes an input terminal,an analog front-end circuit. The analog front-end circuit is coupled tothe input terminal, and includes a chopper circuit and a charge pumpcircuit. The charge pump circuit includes a voltage output terminal, aflying capacitor, and a current source. The voltage output terminal iscoupled to the input terminal and the chopper circuit. The flyingcapacitor includes a first terminal coupled to the voltage outputterminal, and a second terminal coupled to an output terminal of a drivecircuit. The current source includes a first terminal coupled to thevoltage output terminal, and a second terminal coupled to a power supplyrail.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a schematic diagram for an example charge pump circuit withundervoltage regulation in accordance with this description;

FIG. 2 shows a block diagram for an example control circuit suitable foruse in a charge pump circuit in accordance with this description;

FIG. 3 shows a schematic diagram for another implementation of a chargepump circuit with undervoltage regulation in accordance with thisdescription;

FIG. 4 shows a schematic diagram for an example charge pump circuit withovervoltage protection in accordance with this description; and

FIG. 5 shows an example electronic circuit that includes a charge pumpcircuit in accordance with this description.

DETAILED DESCRIPTION

In this description, the term “couple” or “couples” means either anindirect or direct wired or wireless connection. Thus, if a first devicecouples to a second device, that connection may be through a directconnection or through an indirect connection via other devices andconnections. Also, in this description, the recitation “based on” means“based at least in part on.” Therefore, if X is based on Y, then X maybe a function of Y and any number of other factors.

Some charge pump circuits have no current capability or have high outputresistance in the direction of reverse current flow. For example, acharge pump circuit that provides negative output voltage may be unableto source current. Consequently, such charge pump circuits may beintolerant to excess voltage arising from external sources. Excessvoltage may damage the charge pump circuit or circuitry powered by thecharge pump circuit.

The charge pump circuits disclosed herein include circuitry forregulating the voltage at the output of the charge pump circuit toprevent overvoltage or undervoltage caused by external circuitry. Chargepump circuit implementations include a voltage inverting circuit togenerate a negative voltage and current source that passes a current tothe output of the charge pump circuit when voltage at the output fallsbelow a desired voltage. The current source and the voltage invertingcircuit are controlled by a control circuit (e.g., a class B or class ABcontrol circuit) that receives output voltage error information from anerror amplifier. The charge pump circuits of the present disclosure donot require Zener diodes (which are not available in all semiconductorprocesses) for protection or voltage regulation, and are suitable foruse with high-impedance analog inputs.

FIG. 1 shows a schematic diagram for an example charge pump circuit 100with overvoltage regulation in accordance with this description. Thecharge pump circuit 100 includes a voltage inverter circuit 102, acurrent source 103, a control circuit 106, an error amplifier 108, and avoltage output terminal 118. The voltage inverter circuit 102 is coupledto the voltage output terminal 118 and the control circuit 106, andgenerates a negative voltage at the voltage output terminal 118 based ona positive voltage provided at the power supply rail 120. For example,if +3.3 volts is provided at the power supply rail 120, then the voltageinverter circuit 102 provides −3.3 volts (approximately) at the voltageoutput terminal 118.

The voltage inverter circuit 102 includes a driver circuit 110, a flyingcapacitor 112, a transistor 114, and a switch 116. An input terminal1106 of the driver circuit 110 is coupled to a clock source (e.g., anoscillator circuit), and an output terminal 110A of the driver circuit110 is coupled to a terminal 112A of the flying capacitor 112. Thedriver circuit 110 charges the flying capacitor 112 by driving thevoltage provided at the power supply rail 120 onto the terminal 112Aduring a first part 124 of a clock cycle, and connects the terminal 112Ato the drain terminal 114D of the transistor 114 during a second part122 of the clock cycle.

The flying capacitor 112 is coupled to the voltage output terminal 118and to a ground rail 132 via the switch 116. The ground rail 132 is apower supply rail coupled to a common voltage source. The switch 116includes a terminal 116A coupled to a terminal 112B of the flyingcapacitor 112, a terminal 116B coupled to the voltage output terminal118, and a terminal 116C coupled to the ground rail 132. The switch 116may be implemented as two switches disposed in parallel. In the firstpart 124 of the clock cycle, the switch 116 connects the terminal 1126of the flying capacitor 112 to the ground rail 132 for charging, and inthe second part 122 of the clock cycle the switch 116 connects theterminal 112B of the flying capacitor 112 to the voltage output terminal118 for provision of the negative voltage.

The transistor 114 is coupled to the driver circuit 110 and the controlcircuit 106. The transistor 114 controls connection of the drivercircuit 110 to the ground rail 132, and thereby controls the chargetransferred from the flying capacitor 112 to the voltage output terminal118. For example, turning the transistor 114 on harder results intransfer of more charge from the voltage output terminal 118 to theflying capacitor 112. The transistor 114 is an N-channel metal oxidesemiconductor field effect transistor (MOSFET) in some implementationsof the charge pump circuit 100. The transistor 114 includes a drainterminal 114D coupled to a common terminal 110C of the driver circuit110, and a source terminal 114S coupled to the ground rail 132.

The current source 103 includes a transistor 104 that passes a currentto the voltage output terminal 118 when the voltage at the voltageoutput terminal 118 falls below a predetermined threshold voltage (e.g.,the desired output voltage of the charge pump circuit 100). Thus, thetransistor 104 increases the voltage at the voltage output terminal 118when the voltage at the voltage output terminal 118 becomes morenegative than the predetermined threshold voltage. The transistor 104 isa P-channel MOSFET in some implementations of the charge pump circuit100. The transistor 104 includes a drain terminal 104D coupled to thevoltage output terminal 118 and a source terminal 104S coupled to thepower supply rail 120. The transistor 104 is controlled by the controlcircuit 106.

The error amplifier 108 compares (determines a difference of) thevoltage at the voltage output terminal 118 to a reference voltage 128,and generates a difference signal 130 that is dependent on thedifference in the voltage at the voltage output terminal 118 and thereference voltage 128. The error amplifier 108 includes an inputterminal 108A coupled to the voltage output terminal 118 and an inputterminal 108B coupled to the reference voltage source 126. The erroramplifier 108 may include an operational transconductance amplifier insome implementations of the charge pump circuit 100.

The control circuit 106 controls the voltage inverter circuit 102 andthe transistor 104 based on the difference signal 130 received from theerror amplifier 108. The control circuit 106 includes an input terminal106A coupled to an output terminal 108C of the error amplifier 108. Insome implementations of the charge pump circuit 100, the control circuit106 is a class AB control circuit or a class B control circuit. Thecontrol circuit 106 includes an output terminal 106B coupled to the gateterminal 104G of the transistor 104, and an output terminal 106C coupledto the gate terminal 114G of the transistor 114. When the differencesignal 130 indicates that the voltage at the voltage output terminal 118is greater than a voltage desired at the voltage output terminal 118,then the control circuit 106 enables the voltage inverter circuit 102(by turning on the transistor 114) to lower the voltage at the voltageoutput terminal 118. When the difference signal 130 indicates that thevoltage at the voltage output terminal 118 is less than a voltagedesired at the voltage output terminal 118, then the control circuit 106turns on the transistor 104 to increase the voltage at the voltageoutput terminal 118. Thus, if a circuit external to the charge pumpcircuit 100 causes the voltage at the voltage output terminal 118 tofall below the desired voltage at the voltage output terminal 118 (e.g.,causes the voltage at the voltage output terminal 118 to fall below athreshold), then the control circuit 106 turns on the transistor 104 tosource a current (I_(CP)) to the voltage output terminal 118 andincrease the voltage at the voltage output terminal 118. Similarly, ifthe voltage at the voltage output terminal 118 is greater than thedesired voltage (e.g., above a threshold), then the error amplifier 108turns on the transistor 114 to lower the voltage at the voltage outputterminal 118.

FIG. 2 shows a block diagram for an example control circuit 200 suitablefor use in the charge pump circuit 100 in accordance with thisdescription. The control circuit 200 is an implementation of the controlcircuit 106. The control circuit 200 is a Monticelli class AB controlcircuit. Some implementations of the control circuit 200 apply differentcontrol circuitry. The control circuit 200 includes a current source202, a transistor 204, a transistor 206, a voltage source 208, and avoltage source 210. The transistors 204 and 206 are coupled to andcontrol the transistors 104 and 114. The voltage source 208 sets athreshold for turning on the transistor 204 and, in turn, turning on thetransistor 104, and at the same time, the minimum gate voltage for thetransistor 114. As the difference signal 130 drops to level indicatingthat the voltage at the voltage output terminal 118 is below a desiredvoltage, the gate-source voltage of the transistor 204 is sufficient toturn on the transistor 204, thereby reducing the voltage at the gateterminal 104G of the transistor 104. The transistor 206 passes currentto the difference signal 130 when the gate-source voltage of thetransistor 206 is sufficient to turn on the transistor 206 (e.g., whenthe transistor 204 is turned off). The voltage source 210 sets thethreshold for turning on the transistor 206, and at the same time, themaximum voltage at the gate of the transistor 104.

FIG. 3 shows a schematic diagram for an example charge pump circuit 300with overvoltage regulation in accordance with this description. Thecharge pump circuit 300 is similar to the charge pump circuit 100, andreplaces the current source 103 with current source 303. The charge pumpcircuit 300 includes a voltage inverter circuit 102, the current source303, the control circuit 106, the error amplifier 108, and the voltageoutput terminal 118. The voltage inverter circuit 102 is coupled to thevoltage output terminal 118 and the control circuit 106, and generates anegative voltage at the voltage output terminal 118 based on a positivevoltage provided at the power supply rail 120. For example, if +3.3volts is provided at the power supply rail 120, then the voltageinverter circuit 102 provides −3.3 volts (approximately) at the voltageoutput terminal 118.

Operation of the voltage inverter circuit 102, the control circuit 106,and the error amplifier 108 is explained with regard to the charge pumpcircuit 100. Some implementations of the control circuit 106 include thecontrol circuit 200.

The current source 303 passes a current to the voltage output terminal118 when the voltage at the voltage output terminal 118 falls below apredetermined threshold voltage (e.g., the desired output voltage of thecharge pump circuit 300). The current source 303 includes a transistor302, a transistor 304, and a transistor 306. The transistor 304 includesa source terminal 304S coupled to the power supply rail 120, a gateterminal 304G coupled to the output terminal 106B of the control circuit106. When the control circuit 106 determines that the voltage at thevoltage output terminal 118 is lower than the predetermined thresholdvoltage, the control circuit 106 activates the 304. The transistor 304is a P-channel MOSFET in some implementations of the current source 303.

The transistor 302 and the transistor 306 form a current mirror. Thetransistor 306 is connected as a diode. The drain terminal 306D of thetransistor 306 is coupled to the drain terminal 304D of the transistor304 and to the gate terminal 306G of the transistor 306. A sourceterminal 306S of the transistor 302 is coupled to the voltage outputterminal 118. The gate terminal 302G of the transistor 302 is coupled tothe gate terminal 306G of the transistor 306, and the source terminal302S of the transistor 302 is coupled to the voltage output terminal118. The drain terminal 302D of the transistor 302 is coupled to theground rail 332. The transistor 302 and the transistor 306 are scaledsuch that the transistor 306 is N times larger than the transistor 302in some implementations of the current source 303. The transistor 302and the transistor 306 are N-channel MOSFETs in some implementations ofthe current source 303.

When the control circuit 106 activates the transistor 304, current flowsfrom the power supply rail through the transistor 304 and the transistor306 to the voltage output terminal 118. Current flow through thetransistor 306 activates the transistor 302, and N times the currentflowing in the transistor 306 flows from the ground rail 332 through thetransistor 302 to the voltage output terminal 118, thereby increasingthe voltage on the voltage output terminal 118. By drawing current fromground, the current source 303 limits the power dissipated by the chargepump circuit 300, which is advantageous, for example, in battery poweredimplementations of the charge pump circuit 300.

In some implementations of the current source 303, a resistor replacesthe transistor 306. For example, a first terminal of the resistor iscoupled to the drain terminal 304D of the transistor 304 and the gateterminal 302G of the transistor 302, and a second terminal of theresistor is coupled to the voltage output terminal 118.

FIG. 4 shows a schematic diagram for an example charge pump circuit 400with overvoltage protection in accordance with this description. Thecharge pump circuit 400 includes a voltage doubler circuit 402, acurrent source 403, a control circuit 406, an error amplifier 408, and avoltage output terminal 418. The voltage doubler circuit 402 is coupledto the voltage output terminal 418 and the control circuit 406, andgenerates a positive voltage at the voltage output terminal 418 that isapproximately double a positive voltage provided at the power supplyrail 420. For example, if +3.3 volts is provided at the power supplyrail 420, then the voltage doubler circuit 402 provides 6.6 volts(approximately) at the voltage output terminal 418.

The voltage doubler circuit 402 includes a driver circuit 410, a flyingcapacitor 412, a transistor 414, and a switch 416. An input terminal410B of the driver circuit 410 is coupled to a clock source (e.g., anoscillator circuit), and an output terminal 410A of the driver circuit410 is coupled to a terminal 412A of the flying capacitor 412.

The flying capacitor 412 is coupled to the voltage output terminal 418and to the power supply rail 420 via the switch 416. The switch 416includes a terminal 416A coupled to a terminal 412B of the flyingcapacitor 412, a terminal 416B coupled to the voltage output terminal418, and a terminal 416C coupled to the power supply rail 420. Theswitch 416 may be implemented as two switches disposed in parallel. Inthe first part 422 of the clock cycle, the switch 416 connects theterminal 412B of the flying capacitor 412 to the power supply rail 420for charging, and the driver 410 connects the terminal 412A of thecapacitor 412 to ground. In the second part 424 of the clock cycle, theswitch 416 connects the terminal 412B of the flying capacitor 412 to thevoltage output terminal 418, and the driver 410 connects the terminal412A of the capacitor 412 to the drain terminal 414D of the transistor414.

The transistor 414 is coupled to the driver circuit 410 and the controlcircuit 406. The transistor 414 controls connection of the drivercircuit 410 to the power supply rail 420, and thereby controls thecharge transferred from the flying capacitor 412 to the voltage outputterminal 418. For example, turning the transistor 414 on harder resultsin transfer of more charge from the flying capacitor 412 to the voltageoutput terminal 418. The transistor 414 is a P-channel metal oxidesemiconductor field effect transistor (MOSFET) in some implementationsof the charge pump circuit 400. The transistor 414 includes a drainterminal 414D coupled to a terminal 410C of the driver circuit 410, anda source terminal 414S coupled to the power supply rail 420.

The current source 403 includes a transistor 404 that sinks current fromthe voltage output terminal 418 when the voltage at the voltage outputterminal 418 rises above a predetermined threshold voltage (e.g., thedesired output voltage of the charge pump circuit 400). Thus, thetransistor 404 decreases the voltage at the voltage output terminal 418when the voltage at the voltage output terminal 418 becomes morepositive than the predetermined threshold voltage. The transistor 404 isan N-channel MOSFET in some implementations of the charge pump circuit400. The transistor 404 includes a drain terminal 404D coupled to thevoltage output terminal 418 and a source terminal 404S coupled to theground rail 442. The transistor 404 is controlled by the control circuit406.

The error amplifier 408 compares (determines a difference of) thevoltage at the voltage output terminal 418 to a reference voltage 428,and generates a difference signal 430 that is dependent on thedifference in the voltage at the voltage output terminal 418 and thereference voltage 428. The error amplifier 408 includes an inputterminal 408A coupled to the voltage output terminal 418 and an inputterminal 408B coupled to the reference voltage source 426. The erroramplifier 408 may include an operational transconductance amplifier insome implementations of the charge pump circuit 400.

The control circuit 406 controls the voltage inverter circuit 402 andthe transistor 404 based on the difference signal 430 received from theerror amplifier 408. The control circuit 406 includes an input terminal406A coupled to an output terminal 408C of the error amplifier 408. Insome implementations of the charge pump circuit 400, the control circuit406 is a class AB control circuit or a class B control circuit. Thecontrol circuit 406 includes an output terminal 406B coupled to the gateterminal 404G of the transistor 404, and an output terminal 406C coupledto the gate terminal 414G of the transistor 414. When the differencesignal 430 indicates that the voltage at the voltage output terminal 418is less than a voltage desired at the voltage output terminal 118, thenthe control circuit 406 enables the voltage doubler circuit 402 (byturning on the transistor 414) to increase the voltage at the voltageoutput terminal 418. When the difference signal 430 indicates that thevoltage at the voltage output terminal 418 is greater than a voltagedesired at the voltage output terminal 418, then the control circuit 406turns on the transistor 404 to decrease the voltage at the voltageoutput terminal 418. Thus, if a circuit external to the charge pumpcircuit 400 causes the voltage at the voltage output terminal 418 torise above the desired voltage at the voltage output terminal 418 (e.g.,causes the voltage at the voltage output terminal 418 to rise above athreshold), then the control circuit 406 turns on the transistor 404 tosink a current from the voltage output terminal 418 and decrease thevoltage at the voltage output terminal 418. Similarly, if the voltage atthe voltage output terminal 418 is less than the desired voltage (e.g.,below a threshold), then the control circuit 406 turns on the transistor414 to increase the voltage at the voltage output terminal 418.

The control circuit 406 includes a Monticelli class AB control circuit.Some implementations of the control circuit 406 apply different controlcircuitry. The control circuit 406 includes a current source 432, atransistor 434, a transistor 436, a voltage source 438, and a voltagesource 440. The voltage source 438 sets a threshold for turning on thetransistor 434, and the voltage source 440 sets a threshold for turningon the transistor 436. The transistors 434 and 436 are operate as alevel shifter with respect to the gate terminals of the transistors 404and 414. When output current of the error amplifier 408 increases(indicating that voltage at the voltage output terminal 418 exceeds thereference voltage 428), the voltage at the gate terminal 414G of thetransistor 414 increases to turn off the transistor 414, and the voltageat the gate terminal 404G of the transistor 404 increases to turn on thetransistor 404. When output current of the error amplifier 408 decreases(indicating that voltage at the voltage output terminal 418 is less thanthe reference voltage 428), the voltage at the gate terminal 414G of thetransistor 414 decreases to turn on the transistor 414, and the voltageat the gate terminal 404G of the transistor 404 decreases to turn offthe transistor 404.

FIG. 5 shows an example electronic circuit 500. The electronic circuit500 includes an input terminal 502 and an analog front-end circuit 504coupled to the input terminal 502. The analog front-end circuit 504conditions a signal received at the input terminal 502 for furtherprocessing. For example, the analog front-end circuit 504 conditions areceived signal for digitization by an analog-to-digital convertercircuit coupled to an output of the analog front-end circuit 504 in someimplementations of the electronic circuit 500. The analog front-endcircuit 504 includes a chopper-stabilized circuit 506 and a charge pumpcircuit 508. The chopper-stabilized circuit 506 includes input switches509, amplifier 510, and output switches 512. The input switches 509modulate the input signal to reduce the effects of offset and drift inthe amplifier 510. The output switches 512 demodulate the output of theamplifier 510.

The charge pump circuit 508 generates a negative voltage for poweringthe amplifier 510. The charge pump circuit 508 is an implementation ofthe charge pump circuit 100. The voltage output terminal of the chargepump circuit 508 is coupled to an input terminal 506A of the choppercircuit 506. The charge pump circuit 508 is coupled to the inputterminal 502 via the body diodes 513 and 514. External circuitry coupledto the input terminal 502 may sink current sufficient to pull thevoltage 516 below the desired output voltage of the charge pump circuit508. For example, if the desired output voltage of the charge pumpcircuit 508 is −3.0 volts, and circuitry external to the electroniccircuit 500 pulls current through the diodes 513 and 514, then thevoltage 516 may be pulled below −3.0 volts. The excessively low voltagemay damage the amplifier 510 and/or the charge pump circuit 508. Thecharge pump circuit 508 monitors the voltage 516 and if the voltage 516drops below a predetermined threshold voltage (e.g., <−3.3 volts), thenthe charge pump circuit 508 sources current (through the transistor 104)to pull the voltage 516 up to −3.0 volts. Thus, the charge pump circuit508 is capable of both sinking and sourcing current to regulate thevoltage 516.

Modifications are possible in the described embodiments, and otherembodiments are possible, within the scope of the claims.

What is claimed is:
 1. A charge pump circuit, comprising: a voltageoutput terminal; a voltage inverter circuit coupled to the voltageoutput terminal and configured to generate a negative voltage at thevoltage output terminal; and a current source coupled to the voltageoutput terminal and configured to increase a voltage at the voltageoutput terminal responsive to the voltage at the voltage output terminalbeing less than the negative voltage generated by the voltage invertercircuit.
 2. The charge pump circuit of claim 1, further comprising anerror amplifier coupled to the voltage output terminal and a referencevoltage source, and configured to determine a difference of the voltageat the voltage output terminal and a reference voltage.
 3. The chargepump circuit of claim 2, further comprising a control circuit coupled tothe error amplifier, the voltage inverter circuit, and the currentsource, and configured to enable the voltage inverter circuit and thecurrent source responsive to the difference in the voltage at thevoltage output terminal and the reference voltage.
 4. The charge pumpcircuit of claim 3, wherein the control circuit is configured to enablethe current source based on the voltage at the voltage output terminalbeing less than the negative voltage generated by the voltage invertercircuit.
 5. The charge pump circuit of claim 3, wherein the controlcircuit is configured to enable the voltage inverter circuit based onthe voltage at the voltage output terminal being greater than thenegative voltage.
 6. The charge pump circuit of claim 3, wherein thecontrol circuit is a class AB control circuit or a class B controlcircuit.
 7. The charge pump circuit of claim 1, wherein the voltageinverter circuit comprises: a drive circuit coupled to the controlcircuit; a flying capacitor comprising a first terminal coupled to thedrive circuit; and a switch comprising: a first terminal coupled to thevoltage output terminal; a second terminal coupled to a second terminalof the flying capacitor; and a third terminal coupled to a power supplyrail.
 8. An electronic circuit, comprising: an input terminal; and ananalog front-end circuit coupled to the input terminal, and comprising:a chopper circuit; and a charge pump circuit comprising: a voltageoutput terminal coupled to the input terminal and the chopper circuit; aflying capacitor comprising: a first terminal coupled to the voltageoutput terminal; and a second terminal coupled to an output terminal ofa drive circuit; and a current source comprising: a first terminalcoupled to the voltage output terminal; and a second terminal coupled toa power supply rail.